In making the 134th trade since he bought the team in 1989 and his 60th draft day trade, Cowboys owner Jerry Jones swapped first-round picks with the San Francisco 49ers.

The defending NFC champs received the 18th overall pick from Dallas. In addition to getting the 31st pick, the Cowboys received the 74th overall pick, giving them three selections in the third round and seven total picks.

“We were unanimous it was the smart thing to do after all the homework we had done,” Jones said.

Dallas entered the draft with only six picks after trading its seventh rounder to Miami last year to acquire offensive lineman Ryan Cook.

“We didn't see a player we wanted to spend that pick (No. 18) on,” Jones said. “The incentive was to end up with a third-round pick and a first-round player (at No. 31). We think that's what we did.”

Jones said the Cowboys gave first-round grades to 19 players. Frederick was No. 22 on their board.

In the 6-foot-31/2, 320-pound Frederick, the Cowboys selected a player known for his high football IQ and thick upper body. But he had a third-round grade from NFLDraftScout.com and is susceptible to explosive interior defensive lineman. That could be bad news for quarterback Tony Romo, who often struggles to escape pressure up the middle.

“I was a little surprised,” Frederick said of being chosen by Dallas. “I thought I would fit somewhere in the second round, but Dallas showed a lot of interest in me throughout the process. I know they need help inside, so I think I will fit in well down there.”

The 49ers selected Reid with the 18th pick. The New York Giants took Pugh with the 19th. Minnesota grabbed Floyd with the 23rd and Denver lassoed Williams with the 28th.

Asked why Dallas passed on taking a defensive lineman to aid Monte Kiffin in changing the team's scheme from a 3-4 to a 4-3 alignment, Jones said, “We put an emphasis on the interior of our offensive line. We feel like defensive line is a position of strength.”

Given a win-now ultimatum by Jones in February, Garrett appeared to be disappointed by the deal. The coach told reporters recently the further you trade down the further you move away from a good player.

DallasCowboys.com displayed a live video of the action in the Cowboys' draft room, allowing fans and the media to watch Jones, Garrett and chief scout Tom Ciskowski in action. In the moments before and after the trade was announced, Garrett's body language and facial expressions seemed to indicate he wasn't pleased.

But Garrett indicated later he was on board with the deal.

“There is a lot to like about (Frederick),” Garrett said. “He has position (versatility). He's a smart, tough guy. He has good makeup as a person. ... And we feel like the third round is rich with players.”

The Cowboys signed center Phil Costa, 25, to a two-year deal in March even after he logged only three starts in 2012 due to back and ankle injuries. Cook started 11 games at center last season.